Method and apparatus for quickly erecting off-shore platforms

The method of quickly elevating a drilling and production platform relative to a plurality of bottomed, upright caissons having the upper end thereof projecting above the water to a height greater than that to which the platform is to be elevated, and wherein the platform has a plurality of open caisson wells, one for each caisson, and is movable into position to receive said caissons, and wherein the platform has a jacking unit for each caisson, and wherein each of the jacking units includes a horizontal jacking head, two pairs of jacking legs, said pairs of jacking legs being pivotally connected at the upper end thereof to the respective opposite ends of the jacking head, and four jacking mechanisms, each pivotally connected at the lower end thereof to the platform and receiving one of the jacking legs, the steps comprising:

• holding the jacking heads at an elevation higher than the upper end of the caissons;
• positioning the platform so that a caisson is received in each of the caisson wells;
• lowering the jacking heads, and sliding the jacking legs downwardly through their associated jacking mechanisms until the jacking heads engage the upper end of the caissons;
• and then operating the jacking mechanisms of the jacking units to hoist the platform on the caissons, utilizing the upper end of the caissons as load reaction points for the hoisting effort of the jacking units.

The method of lifting a buoyant off-shore platform on a pre-installed support, by means of a fail-safe jacking mechanism attached to said platform and positioned on an elongated jacking leg connected at its upper end to said support, under conditions in which said platform is subject to wave action, said jacking mechanism including upper and lower housings having therein upper and lower sets of wedge-shaped, self-energizing slips, respectively, arranged to sequentially grip and release said elongated jacking leg to provide a ratchet-like action, said upper and lower housings being connected together by jacking means disposed therebetween and said lower housing being attached to said platform, and wherein said method comprises the steps of:

• actuating said jacking means to apply jacking forces between said housings for sequentially moving said housings toward and away from each other, and upwardly relative to said jacking leg to cause said sets of slips to selectively grip or release said jacking leg;
• moving the upper housing upwardly away from the lower housing to release the upper set of slips while maintaining the lower set of slips energized in a gripping, fail-safe condition;
• next moving said lower housing upwardly toward said upper housing to cause the upper set of slips to grip said jacking leg to establish a fail-safe condition and to lift said platform relative to said jacking leg, and to release the grip of the lower set of slips, whereby any effective wave action occurring during said lifting of said platform will assist in raising said platform, and said upper set of slips will hold said platform at the position to which it has been raised by said wave action and will continue to raise said platform so long as said lower housing is being moved upwardly toward said upper housing, and whereby the maintenance of said slips in a fail-safe condition prevents accidental dropping of said platform.

Apparatus comprising a support, an elongated jacking leg connected to said support, a buoyant offshore platform subject to wave action and a jacking mechanism positioned on said jacking leg and connected to said platform, said jacking mechanism including first and second gripping means for gripping said jacking leg, each of said gripping means including a set of wedge-shaped, spring-actuated, self energizing slips mounted in a correspondingly shaped slip holder, said slip holders each being configured and oriented such that the slips of one set automatically grip said jacking leg when a downward force is applied to the slip holder of said one set and automatically release from said jacking leg against said spring actuation when an upward force is applied to said one slip holder, said jacking mechanism further including jacking means positioned between said first and second gripping means for alternately applying jacking forces between said gripping means to move said gripping means toward and away from each other for raising the platform, wherein upwardly directed forces applied to said platform by wave action temporarily release the engaged gripping means against said spring actuation and move same and said platform upwardly along said jacking leg, and wherein immediately upon termination of the application of jacking and/or wave action forces, the associated spring-actuated selfenergizing slips grip said jacking leg to retain the platform at the position to which it has been raised.